The invention concerns an electronic switch with a field effect transistor (FET). The electronic switch serves for rapid switching of broadband, high frequency signals of high amplitude dynamics.
Electronic switches, for example, are employed in high frequency technology in signal attenuators with switchable attenuation stages. To this purpose, mostly FETs are used, connected in series, or for very high frequency and broadband applications, metal, semiconductor field effect transistors (MESFET) are employed. The bandwidths run, for example, from 1 GHz up to several multiples of 10 GHz. Usually, n-channel-MESFET on a gallium arsenide basis is chosen.
Such an electronic switch, for example, is made known by U.S. Pat. No. 5,107,152. The circuit disclosed in that patent, with the aid of a diode connected in series with a control port, attempts to improve the low frequency, large signal behavior of the switch, which is governed essentially by the voltage drop over the capacitive portion of the Source-Gate-region and the Drain-Gate-region, respectively.
The disadvantage found in the electronic switch as taught by U.S. Pat. No. 5,107,152 lies therein, in that because of the diodes, the switching time of the electronic switch is essentially increased. In addition to this, the diode improves only one of the two states of the electronic switch.
For the improvement of the low frequency, large signal behavior, further measures can be considered. For example, the gate series resistance can be increased, whereby, however, the switching time would clearly be longer. Finally, the pinch-off voltage of the FETs can be increased by modification of the manufacture process, whereby, especially in the case of MESFETs, narrow limits are imposed by the limited voltage sustaining capability of metal-semiconductor junctions when operated in reverse direction.
On this account it is the purpose of the invention to disclose an electronic switch, which, independently from the characteristics of the input signal, assumes the desired switching state quickly and reliably and holds itself in the chosen state.